This description relates to buck-boost DCxe2x80x94DC switching power conversion, e.g., in converters for which the input operating voltage delivered to the converter may span a range of values extending below and above the magnitude of the DC voltage delivered at the output of the converter.
Electrical and electronic equipment and systems often require conversion of an input voltage to an output voltage, which may be higher or lower than or approximately the same as the input voltage. For example, in stationary or portable systems powered by a DC battery it is often necessary to maintain constancy of output voltages independently of the state of charge and voltage of the battery. As another example, in systems utilizing the new power distribution architecture described in Vinciarelli, U.S. patent application Ser. No. 10/006481, xe2x80x9cFactorized Power Architecture with Point of Load Sine Amplitude Convertersxe2x80x9d, filed Jan. 31, 2002 (the ""481 Application) and incorporated in its entirety by reference, it may be necessary to pre-regulate the xe2x80x9cfactorized bus voltagexe2x80x9d delivered by a pre-regulator module (or xe2x80x9cPRMxe2x80x9d, as that term is used in the ""481 application) to point-of-load voltage transformation modules (or xe2x80x9cVTMsxe2x80x9d, as that term is defined in the ""481 application) by stepping up or down voltage from an input source. As another example, in systems powered from an AC voltage source it is often necessary to draw power from the AC source with near unity power factor while delivering power at a DC output voltage which may be higher or lower than the instantaneous voltage of the AC line. In general, it would be desirable to flexibly achieve the appropriate step up or step down of a voltage with high conversion efficiency, high power density, and low noise.
Buck-boost converters are known in the art. The buck-boost converter 10, shown in FIG. 1A, for example, is described in Severns and Bloom, xe2x80x9cModern DC-to-DC Switchmode Power Conversion Circuits,xe2x80x9d 1985, ISBN 0-442-21396-4, pp. 156-157. In the converter of FIG. 1A the switches 2,3 are operated synchronously: switch 2 is in position xe2x80x9cAxe2x80x9d when switch 3 is in position xe2x80x9cAxe2x80x9d and vice versa. Energy delivered from the input source 6 is stored in inductor 4 when switch 2 and 3 are in the xe2x80x9cAxe2x80x9d position and energy is delivered from the inductor to the load 5 when switch 2 and 3 are in the xe2x80x9cBxe2x80x9d position. As also explained in Severns and Bloom, ibid., pp. 157-158, the converter of FIG. 1A may be reduced to a single switch buck-boost converter 12 of FIG. 1B, in which the output voltage, Vo, has a polarity inversion relative to the input source.
In both cases, owing to substantial losses in the inductor and switching elements, the converter architectures of FIG. 1A and FIG. 1B are inefficient relative to other architectures, such as a buck converter or a boost converter which are only capable of, respectively, step-down or step-up of an input voltage. In fact, it has been tempting to conclude that the ability to provide both step-down and step-up of voltage within the same converter comes at a price in terms of reduced efficiency and power density.
This expectation has not been altered by more recent developments. A buck-boost converter incorporating four switches is described in an October 2001 datasheet for the LTC3440 xe2x80x9cMicropower Synchronous Buck-Boost DC/DC Converterxe2x80x9d integrated circuit manufactured by Linear Technology Corporation, Milpitas, Calif., U.S.A. A simplified schematic of the converter circuit 14 is shown in FIG. 2. In the Figure the converter operates in a continuous conduction (i.e., the current in the inductor 23, IL is nonzero throughout the entire operating cycle). A switch controller 19 operates the four MOSFET switches 11,13,15,17 in one of three modes: (1) in a buck mode, with switch 15 always closed and switch 17 always open, when the magnitude, Vin, of the input voltage source 6 is within a range of values which are greater than the voltage, Vo, delivered to the load; (2) in a boost mode, with switch 11 always closed and switch 13 always open, when the magnitude, Vin, of the input voltage source is within a range of values which are less the voltage, Vo; and (3) in a buck-boost mode, with a first pair of switches, 11 and 13, xe2x80x9cphasing inxe2x80x9d to achieve a minimum duty cycle for switch 13, as a second pair of switches, 15 and 17, xe2x80x9cphases outxe2x80x9d to reduce to zero the duty cycle of switch 17, as the magnitude, Vin, of the input voltage source traverses a range of values which bracket the value Vo. As such, this xe2x80x9cbuck-boostxe2x80x9d architecture merely bridges a transition from the boost architecture to the buck architecture, while incurring increased losses and an intermediate reduction of efficiency relative to boost and buck modes that it is bridging. Owing to continuous conduction in the inductor, in each of the three modes referenced above switching losses occur when certain switching elements are turned ON to carry current without the voltage across the switching element being reduced prior to turn ON. Even at light load, where continuous conduction cannot be maintained with a finite value of inductor 23, a lossy damper circuit, comprising switch 16 and xe2x80x9canti-ringxe2x80x9d resistor 18, is included to dissipate energy stored in the parasitic capacitances of the inductor and the switches.
Clamp circuitry for preventing oscillatory noise in switching power converters by using a switch to trap energy in an inductive element and release it to reduce switching losses is described in Vinciarelli et al, U.S. patent application Ser. No. 09/834,750, xe2x80x9cLoss and Noise Reduction in Power Convertersxe2x80x9d, Apr. 13, 2001 (the xe2x80x9c""750 Applicationxe2x80x9d), assigned to the same assignee as this application and incorporated in its entirety by reference.
In general, in one aspect, the invention features apparatus to operate at a power level within a range of power levels that includes a rated maximum power level of the apparatus. The apparatus includes circuit elements to deliver power at an output voltage to a load from a source at an input voltage using an inductor selectively connected between the source and the load during a power conversion cycle. The inductor conducts a current having an average positive value during the power conversion cycle. A first switching device is interposed between the source and a first terminal of the inductor. A second switching device is interposed between a second terminal of the inductor and the load, and a switch controller to turn ON the first switching device during a time interval within the power conversion cycle during which the current is negative.
Implementations of the invention may include one or more of the following features. The input voltage is within a range of input voltages that is less than the output voltage. The input voltage is within a range of input voltages that is greater than the output voltage. The input voltage is within a range of input voltages that includes the output voltage. The first switching device is turned ON at a time when the voltage across the first switching device is less than the input voltage. The first switching device is turned ON at a time when the voltage across the first switching device is essentially zero. The apparatus of claim also includes a third switching device interposed between ground and the first terminal of the inductor, the switch controller controlling the opening and closing of the third switching device. The third switching device is turned ON at a time when the voltage across the third switching device is less than the input voltage. The second switching device comprises a rectifier. The second switching device is turned ON at a time when the voltage across the second switching device is less than the output voltage. The apparatus also includes a fourth switching device interposed between ground and the second terminal of the inductor, the switch controller controlling the opening and closing of the fourth switching device. The fourth switching device is turned ON at a time when the voltage across the fourth switching device is less than the output voltage. The fourth switching device is turned ON at a time when the voltage across the fourth switching device is essentially zero. The switching devices comprise MOSFETs.
The power conversion cycle includes phases. The duration of at least one of the phases is controlled as a function of load. The duration of at least one of the phases is controlled as a function of a difference in magnitude between the input voltage and the output voltage and the maximum duration of the power conversion cycle is constrained to limit the minimum frequency of a succession of the power conversion cycles. The duration of the power conversion cycle increases as the power level decreases. The minimum and maximum durations of the power conversion cycle are constrained to limit the maximum and minimum frequencies of a succession of the power conversion cycles. The phases comprise a clamped phase. The duration of the clamped phase is minimized at the rated maximum power level. The phases comprise an in-out phase. The duration of the in-out phase increases as the magnitude of the difference between the input voltage and the output voltage decreases and the maximum duration of the power conversion cycle is constrained to limit the minimum frequency of a succession of the power conversion cycles. The phases comprise a free-wheel phase. The phases comprise an input phase. The duration of the input phase decreases as the input voltage increases. The duration of the input phase increases as the load increases. The power conversion cycle uses the same sequence of phases regardless of whether the input voltage is above, below, or the same as the output voltage. The apparatus has a power density greater than 200 Watts/cubic inch. The apparatus has a conversion efficiency greater than 97% at an operating condition within the range of power levels. The apparatus has a conversion efficiency greater than 97% when the input voltage level is within 10% of the output voltage level at the rated maximum power level.
In general, in another aspect, the invention features a method that includes delivering average power within a range of power levels including a maximum power level from a source at an input voltage to a load at an output voltage, selectively connecting an inductor to deliver the average power from the source to the load during a power conversion cycle, the average power flowing from the inductor through a second switching device to the load, and closing a first switching device that is interposed between the source and the inductor during a time interval within the power conversion cycle during which power flows from the inductor through the first switching device back to the source.
In general, in another aspect, the invention features, a method comprising converting power for delivery to a load at an output voltage from a source at an input voltage that can be higher or lower than the output voltage, the power being converted in a switching converter having a power density of at least 200 Watts per cubic inch by storing energy in an inductor operating in a discontinuous mode, with switching occurring at zero voltage.
In general, in another aspect, the invention features apparatus comprising a buck-boost converter to operate at a power level within a range of power levels including a rated maximum power level of the apparatus, and a DC transformer to deliver an output voltage to a load, the buck-boost converter comprising circuit elements to deliver power to the DC transformer from a source at an input voltage using an inductor selectively connected between the source and the DC transformer during a power conversion cycle, the inductor conducting a current having an average positive value during the power conversion cycle, a first switching device interposed between the source and a first terminal of the inductor, a second switching device interposed between a second terminal of the inductor and the DC transformer, and a switch controller to turn ON the first switching device during a time interval within the power conversion cycle during which the current in the inductor is negative.
Implementations of the invention may include one or more of the following features. The DC transformer is incorporated in a VTM, the buck-boost converter is incorporated in a PRM, and power is delivered from the PRM to the VTM by a factorized bus. The output voltage of the DC transformer is connected in a feedback configuration to control an operating condition of the buck-boost converter.
In general, in another aspect, the invention features apparatus to operate at a power level within a range of power levels including a rated maximum power level of the apparatus. The apparatus includes circuit elements to deliver power at an output voltage to a load from a source at an input voltage by selectively connecting an external inductor between the source and the load during a power conversion cycle. The inductor conducts a current having an average positive value during the power conversion cycle. A first switching device is coupled to the source and has a port to connect to a first terminal of the inductor. A second switching device is coupled to the load and has a port to connect to a second terminal of the inductor. A switch controller turns ON the first switching device during a time interval within the power conversion cycle during which the current is negative.
Implementations of the invention may include one or more of the following features. The apparatus also includes the inductor. The apparatus comprises an integrated semiconductor device.
In general, in one aspect, the invention features apparatus comprising (a) a buck-boost power converter to operate at a power level within a range of power levels including a rated maximum power level of the apparatus, the buck-boost converter comprising circuit elements to deliver power to a load at an output voltage from an AC source at an input voltage using an inductor selectively connected between the source and the load during a power conversion cycle, the inductor conducting a current having an average positive value during the power conversion cycle, (b) a first switching device interposed between the source and a first terminal of the inductor, (c) a second switching device interposed between a second terminal of the inductor and the load, (d) a switch controller to turn ON the first switching device during a time interval within the power conversion cycle during which the current is negative, and (e) a power factor controller connected to the switch controller to cause the switch controller to control the harmonic content of an input current from the AC source while regulating the output voltage.
Implementations of the invention may include one or more of the following features. The power factor controller receives an input current of the AC source and the output voltage as input signals.
In general, in another aspect, the invention features apparatus comprising (a) a battery, and (b) a power converter connected between the battery and a load to operate at a power level within a range of power levels including a rated maximum power level of the apparatus, the power converter comprising (c) circuit elements to deliver power at an output voltage to the load from the battery at an input voltage using an inductor selectively connected between the battery and the load during a power conversion cycle, the inductor conducting a current having an average positive value during the power conversion cycle, (d) a first switching device interposed between the battery and a first terminal of the inductor, (e) a second switching device interposed between a second terminal of the inductor and the load, and (f) a switch controller to turn ON the first switching device during a time interval within the power conversion cycle during which the current is negative.
In general, in another aspect, the invention features apparatus comprising a buck-boost power converter including (a) a first port to connect to terminals of a device across which a voltage may vary in response to current transients, (b) a second port to connect to a device that stores and releases energy, (c) an inductor to transfer energy between the first port and the second port, the first port and the second port serving selectively as either a source and a load or as a load and a source, (d) switching devices to selectively connect the inductor between any two of the source, the load, and a ground, (e) a switch controller to turn the switches ON and OFF in a sequence to cause power to be converted from the source to the load in either a buck mode or a boost mode, and (d) a port to receive a control input that controls whether the first port and the second port are serving respectively as either the source and the load or as the load and the source.
Implementations of the invention may include one or more of the following features. The apparatus also includes the device that stores and releases energy, e.g., a capacitor.
In general, in another aspect, the invention features apparatus comprising (a) circuit elements to deliver power at an output voltage to a load from a source at an input voltage using an inductor selectively connected between the source and the load during a power conversion cycle, the inductor conducting a current having an average positive value during the power conversion cycle, (b) a first switching device interposed between the source and a first terminal of the inductor, (c) a second switching device interposed between a second terminal of the inductor and the load, (d) a switch controller to turn ON the first switching device during a time interval within the power conversion cycle during which the current is negative, (e) a first port to connect to terminals of an operating device across which a voltage may vary in response to current transients, (f) a second port to connect to a storage device that stores and releases energy, the operating device and the storage device serving selectively either as a source and a load or as a load and a source, and (g) a port to receive a control input that controls whether the first port and the second port are serving respectively as either the source and the load or as the load and the source.
In general, in another aspect, the invention features apparatus adapted to share power within a range of power levels that includes a rated maximum power level of the apparatus, the apparatus comprising (a) circuit elements to deliver power at an output voltage to a load from a source at an input voltage using an inductor selectively connected between the source and the load during a power conversion cycle of a succession of power conversion cycles, the inductor conducting a current having an average positive value during the power conversion cycle and having a negative value during a time interval within the power conversion cycle, (b) a paralleling port to emit or receive from a paralleling bus a paralleling pulse in a succession of paralleling pulses, and (c) a control circuit to synchronize the succession of power conversion cycles to the succession of paralleling pulses.
Implementations of the invention may include the following feature. The paralleling pulse has a rising edge, a falling edge and a pulse width and the control circuit adjusts parameters of the power conversion cycle to parameters of the paralleling pulse.
Other advantages and features will become apparent from the following description and from the claims.